Valve bonnets may be bolted onto the valve body structure if desired and in such event the bonnets may be easily removed for entry into the valve body structure as may be necessary for repair or replacement of the seats and seals.
However, when valve bonnets have been welded and it has been necessary to repair the valve, it has been normal practice heretofore to remove the valve structure from the line and replace it with another valve. While it is possible with a welded valve bonnet to remove the valve bonnet with a cutting tool and to repair the valve in place within the line, then reweld the valve bonnet, this has not been practiced to any extent because of disadvantages such as particles or foreign matter from the cutting operation for removing the bonnet being deposited within the valve body. Also, when the bonnet is rewelded, the welding torch could be exposed to escaping fluid from the line which might be highly inflammable or explosive. Thus, it has not been practical heretofore to repair gate valves, for example, in place within a line.